1. Field of the Invention
This invention relates to internal, expanding drum brakes particularly for use on trailers.
For a trailer it is desirable to make a brake operate so that the braking torque when the drum is rotating in one direction is much lower than it is when the drum is rotating in the other direction. For example, a trailer brake operated by an overrun mechanism will lock-up if the trailer is reversed up a steep gradient. It is therefore desirable to provide a trailer brake which will produce a low braking torque in reverse but full braking torque when operated during forward movement. Such trailer brakes are already known.
2. Description of the Prior Art
For example it is known to have compound shoes each comprising an inner and an outer part which are relatively movable, the inner parts being operated upon by the actuator and the outer parts carrying the brake linings. During forward rotation the shoes act normally but during reverse rotation the outer parts are moved relative to the inner parts by the reactive forces on the linings and the effective diameter of the shoes is decreased thus requiring a greater movement of the actuator to obtain a given braking torque.
It is also known to have a spring-loaded member associated with one of the brake shoes and which moves against its spring loading during reverse movement to prevent the shoe with which it is associated from providing effective braking torque.
It is an object of the invention to provide an improved brake which is particularly suitable for trailers and which will give full braking torque in forward movement but will give a low torque in reverse due to changes in the reactive forces of the shoes but which may be operated to give full torque by a parking brake without the necessity of having to overcome very strong spring-loading.